This disclosure relates to a sensor for determining the physical profile of temperature rises to a pre-determined temperature. It is capable of providing a profile of temperature rises spreading through an adjacent heated element. The device further serves as an indictor of liquid level in systems subjected to overheating.
This invention arose from tests requiring measurement of selected operational parameters within nuclear fuel bundles. It meets projected fuel bundle instrumentation requirements for development of elevated temperature profiles along the length of a fuel bundle. This is desirable in the design, testing and use of a fuel bundle in order to provide a temperature profile at temperatures approaching that at which fuel rod melt down would occur. Such measurements can be accomplished conventionally by the use of multiple theremocouples but their costs and electrical connector requirements make such use prohibitive in actual practice.
One item of information that has not been available in operating reactors to date is the meltdown temperature profile within a core. The present invention is capable of developing this profile during test operation of instrumented fuel bundles for guidance of those designing future reactors. A second important parameter in such tests to meltdown temperatures is measurement of water level in the reactor or in a specific test bundle. The present disclosure will provide both types of information and will provide continuous readout up to a very high temperature at which the device would be destroyed. Even is this extreme case, some readout capability will be retained by that portion of the sensor which is not destroyed.
The present device utilizes two or more elongated electrical conductors arranged so as to be positionable immediately alongside fuel rods or other elongated elements. It includes a plurality of gas-filled expandable conductors fixed at discrete locations along the conductors. Each expandable conductor is independently movable relative to the conductors between a first position in which an open circuit exists across it and a second position in which it operably bridges the conductors in a low resistance circuit. The changes in resistance between the two conductors that result from such bridging can be monitored and measured from both ends of both conductors to provide a temperature profile that indicates the spread of the preselected temperature. Furthermore, when the active length of the device is at least partially submerged in overheated or boiling liquid, the resulting temperature profile serves as an effective indication of liquid level, since a very distinct difference occurs between the temperature of the boiling liquid and the temperature of the vapors or gases immediately above its surface.